1. Technical Field
The present invention relates to an optical disc system used to record data on and/or read data from an optical disc, and more particularly, to an apparatus and method for detecting a type of an optical disc inserted into an optical disc system and/or adjusting track balance.
2. Description of the Related Art
It is known that an optical disc system reads data from an optical disc such as a compact disc (CD) or a digital video disc (DVD), or record data on a CD-rewritable (CD-RW). The optical disc system uses a laser beam to radiate onto the optical disc and an optical pickup to detect variations in the strength of the laser beam reflected from the optical disc. The varied strengths detected are converted to digital data read from the optical disc. The optical disc system adjusts the track balance before reading data from the optical disc inserted into the optical disc system. The optical disc system calculates a track unbalance value from a tracking error signal to adjust the track balance.
FIG. 1 shows a circuit diagram of a conventional tracking error signal generator used in a general optical disc system. Referring to FIG. 1, a tracking error signal generator 20 includes photodiodes 21 and 22, current-to-voltage (I/V) converters 23 and 24, a differential amplifier 25, and resistors Rf and Rv.
The photodiodes 21 and 22 generate currents IF and IE, respectively, in response to F and E beams, which are reflected light detected by an optical pickup.
The I/V converters 23 and 24 convert the currents IF and IE into voltages VF and VE, respectively. The I/V converters 23 and 24 may be amplifiers having gains which are respectively adjusted by the values of the resistors Rf and Rv.
The differential amplifier 25 amplifies a difference between the voltages VF and VE to output the difference as a tracking error signal TE.
The F and E beams are sub beams which are arranged before and after a moving direction of a main (M) beam used for reproduction of a data signal to detect the tracking error signal TE. The M beam moves along a pit row.
FIGS. 2A and 2B show waveforms of the tracking error signal TE generated by the tracking error signal generator 20. The tracking error signal TE is divided into a positive tracking error signal and a negative tracking error signal based on a reference voltage VREF. It is preferable that a peak voltage +VTEPK of the positive tracking error signal and a peak voltage −VTEPK of the negative tracking error signal are symmetrical with respect to the reference voltage VREF, as shown in FIG. 2A. If the peak voltage +VTEPK of the positive tracking error signal and the peak voltage −VTEPK of the negative tracking error signal are asymmetrical with respect to the reference voltage VREF, a margin of one of the positive and negative tracking error signals of the tracking error signal TE is reduced. In FIG. 2B, a margin of the negative tracking error signal is narrower than a margin of the positive tracking error signal.
When a margin of the tracking error signal TE is reduced, a range of controlling tracks is reduced and tracks beyond the range cannot be controlled.
As shown in FIG. 2B, a central voltage VTEC of the tracking error signal TE is offset with respect to the reference voltage VREF due to a difference between amounts of the F and E beams and a difference between gains obtained by the I/V converters 23 and 24.
Accordingly, to make the tracking error signal TE symmetrical with respect to the reference voltage VREF, a track balance adjustment is needed to allow the central voltage VTEC of the tracking error signal TE to coincide with the reference voltage VREF.
FIG. 3 shows a flowchart 100 of a conventional method of adjusting a track balance in an optical disc system. FIG. 4 shows a waveform of a tracking error signal produced by the method of FIG. 3.
Referring to FIGS. 3 and 4, in step 101, an optical disc system detects a tracking error signal TE. In step 102, a determination is made as to whether the tracking error signal TE satisfies predetermined conditions. When the tracking error signal TE does not satisfy the predetermined conditions of a predetermined frequency range and a predetermined amplitude range TLength, the tracking error signal TE is filtered in step 103.
In step 103, a determination is made as to whether intersections between the tracking error signal TE and the reference voltage VREF are rising edges of the tracking error signal TE indicated by A, B, C, and D shown in FIG. 4.
If the determination is made that the intersections between the tracking error signal TE and the reference voltage VREF are the rising edges, in step 104, a peak value +VTEPK of a positive tracking error signal is detected. A greater value obtained from a comparison between a previously received tracking error signal TE and a subsequently received tracking error signal TE is updated as the peak value +VTEPK. Successively received tracking error signals TE are continuously compared to detect a maximum value as the peak value +VTEPK.
In step 105, a peak value −VTEPK of a negative tracking error signal is detected. The peak value −VTEPK can also be updated by continuously comparing successively received tracking error signals TE.
In step 106, an average value of the peak values +VTEPK and −VTEPK is calculated using Equation of AVTE1=(+VTEPK and −VTEPK)/2.
In step 107, a determination is made as to whether a peak value of the tracking error signal TE is measured a predetermined number of times (N), where N is a natural number. If in step 107, the determination is made that the peak value of the tracking error signal TE is not measured N times, the optical disc system returns to step 101 to repeat steps 101 through 107.
If in step 107, the determination is made that the peak value of the tracking error signal TE reaches N times, in step 108, an average value of average values AVTE1 through AVTEN calculated during the N-time measurements is determined as an unbalance value UBAL.
In step 109, a determination is made as to whether the unbalance value UBAL satisfies an allowable error. If in step 109, the determination is made that the unbalance value UBAL does not satisfy the allowable error, in step 110, the optical disc system outputs a balance control signal BAL_CTL. The balance control signal BAL_CTL is used to adjust a gain of the tracking error signal generator 20 shown in FIG. 1, after a predetermined period of time TBwt, and returns to step 101. As shown in FIG. 4, the predetermined period of time TBwt refers to a time for which the tracking error signal TE is stabilized after the gain of the tracking error signal generator 20 is adjusted.
If in step 109, the determination is made that the unbalance value UBAL satisfies the allowable error, in step 111, the optical disc system stops controlling the balance of the tracking error signal TE.
In the above-described track balance adjusting method, the unbalance value UBAL is detected using only the peak values +VTEPK and −VTEPK of the tracking error signal TE. Errors may occur in the peak values +VTEPK and −VTEPK due to noise. Also, the frequency range, the amplitude range TLength, and the predetermined number, N, peak values +VTEPK and −VTEPK must be properly set.
The optical disc system also performs a focus search to discern between a CD and a CD-RW. A focus error signal appears in an S-Curve form. A greater absolute value may be obtained from a comparison between absolute values of positive and negative peaks of S-Curves and then compared with a detecting level of the CD-RW to detect the type of an optical disc inserted into the optical disc system.
FIGS. 5A and 5B show graphs used for detecting a disc type according to the conventional art. FIG. 5A shows an output signal FOD output of a focus servo to move a lens. FIG. 5B shows a focus error (FE) signal indicating an amount of light reflected from an optical disc, where the FE signal is also called S-Curves. A peak value of a FE signal detected from a CD is different from a peak value of a FE signal detected from a CD-RW. Accordingly, for detection of a disc type, a positive peak value of the FE signal is compared with a negative peak value of the FE signal to select the greater absolute value, and then the greater absolute value is compared with a predetermined disc detection level DDT_J. When the selected absolute value is less than the disc detection level DDT_J, the disc type is determined as the CD-RW. When the selected absolute value is greater than the disc detection level DDT_J, the disc type is determined as the CD.
The FE signal may be offset when the disc type is detected using the peak values of the FE signal, which affects the detection of the disc type. For example, in a case where the FE signal detected from the CD-RW is offset, and thus a positive peak value of the FE signal is greater than the disc detection level DDT_J, the CD-RW is mistakenly detected as the CD. In addition, a glitch may occur in the FE signal due to noise and thus be misinterpreted as a peak value, which results in the erroneous detection of the disc type.
In addition, for the accurate detection of the disc type, the peak value of the FE signal may be measured several times. In this case, an average value of the peak values may be calculated to detect the disc type using the average value to accurately detect the disc type. However, this process increases read-in time.
Accordingly, when a peak value of a tracking error signal or a focus error signal is detected to adjust a track balance in an optical disc system or detect a type of an optical disc inserted into the optical disc system, the track balance may be wrongly adjusted or the type of the optical disc may be mistakenly detected due to offset or noise components of the track error signal or the focus error signal.
Therefore, a need exists for a system and method for stably adjusting the track balance and accurately detecting the type of the optical disc with reduced read-in time.